Severe WX March 23-25th, 2023

[Tanner]

I mean failure modes are always looming in weather lol especially mesoscale wise. There was a minority(small, but not insignificant amount) of folks on another severe wx board that were insistent the entire week building up to 4/27 that either the convection in the morning would sap the atmosphere, or another mode I can’t think of at this time. Fred was insistent throughout that the “crapvection” wouldn’t harm the later threat.

And disclaimer, I’m not comparing this to 4/27 at all, I’m just saying even the gold standard of set ups will have some failure modes leading up to the event.

And it was the big events like 4/27 that caught everyone off guard because no matter how much preparedness goes into a high-end event, there is always questions that linger until mere hours prior to it. Impending doom scenario...hahaha.

 

[ColdFront]

I think the biggest question for me going into this event is the LLLR, as have been the last several big setups. Models such as the RAP and the NAM are not showing impressive low level lapse rates, which is sufficient in storm development and sustainability. Right now, as it stands, I think the mesoscale features such as surface heating will be the determining factor in how tomorrow plays out.

Sigh...I hate having so much uncertainty the day before a weather event.

Agreed. LLLRs have been putrid the last few set ups, however, I think this one has the best chance out of the last few to turn that trend around surface heating wise.


If you watch Trey’s analysis on the 5/20/2019 event under performing event (won’t use the B word) besides the stout cap, weak LLLRs also played a role in that under performing.

 

[CentralKyWeather]

This system reminds me alot of the one on March 3rd this year. If there is a break in the action Friday afternoon i see numerous spinups just Southeast of the Low.

 

[ashtonlemleywx]

NAM 3k seems to hint at a preconfluence band forming well ahead of the rest of the convection. Don't be surprised to see a few discrete cells in Mississippi ahead of the main blob of convection a few hours before Sunset.

Those early preconfluence bands have snuck up on me so many times. It'll form before I plan to leave and I'll have to rush out to door as quick as I can once it pops up on radar. CAMs have struggled lately picking up on these early cells.

 

[JBishopwx]

Latest Discussion:

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE LOWER MISSISSIPPI VALLEY...

...SUMMARY...
Severe thunderstorms are likely from the Lower Mississippi Valley
toward the lower Ohio Valley Friday afternoon and evening.
Tornadoes, some strong, as well as damaging winds and hail are
expected.

...Synopsis...
A shortwave trough with positive tilt will move across the Southern
Plains on Friday, and into the middle MS/lower OH Valley by Saturday
morning. The primary zone of cooling aloft will remain roughly along
and north of a Texarkana to Memphis to Evansville line, but height
falls will occur even south of the jet core toward the northern Gulf
Coast. This wave will impinge upon a prominent upper high over the
Southeast, with a leading anticyclonically curved jet lifting north
across the OH River and toward the Upper Great Lakes.

The combination of differential divergence and low-level warm
advection looks to be maximized from the Ozarks into the lower OH
Valley from 21 to 06Z. Coincidentally, the surface low will deepen
most after 00Z as it moves from northern AR northeastward up the OH
Valley overnight. The low will move along an existing synoptic
front, with a northward-jumping warm front possible just ahead of
the low track from far southeast MO/southern IL into southern IN
after 00Z. A cold front will develop behind the low, with low-level
convergence maximized from northeast TX into western AR by 00Z,
pushing east across northern MS and western TN/KY after 06Z. More
subtle convergence is anticipated over southern portions of the warm
sector across the Sabine River and into LA.

The warm sector will be characterized by mid 60s F dewpoints from
the low track southward, with upper 60s to 70 F likely into northern
LA and central MS. Strong deep-layer shear will overspread the
region, with increasing low-level shear developing late in the
day/evening from the lower MS valley to the OH Valley as 850 winds
increase into the 50-70 kt range.

...Western and northern AR into the OH Valley...
Early day storms will be ongoing from eastern OK across northern AR
and toward the OH River along and north of a surface front in a zone
of glancing warm advection with a veered low-level jet. Some of this
activity could contain hail from OK into AR given elevated MUCAPE
over 1000 J/kg and long hodographs.

In the wake of the earlier activity, diurnal storms are expected to
form near the surface low and front extending south across western
AR by mid afternoon, with additional activity extending
northeastward along the developing warm front into southeast MO and
to the OH River. Supercells may mature over AR, producing tornadoes
especially later in the day toward 00Z as the low-level jet
strengthens rapidly. This threat will expand quickly northeastward
across the OH Valley, with a corridor of tornado or damaging winds
anticipated near the surface low track. Given the very strong shear
Friday evening, minimal uncapped surface-based instability will be
needed to produce significant severe storms. As additional model
guidance arrives and better observations exist into the Day 1
period, it is plausible that parts of the Moderate Risk could be
extended/shifted northward a bit across AR given the more favorable
large-scale lift over northern areas.

...Lower MS Valley...
The air mass will destabilize across this area well into the
evening, which will remain open warm sector with the cold front
stalling to the west. Severe weather is most likely late in the day
and evening as low-level moisture remains favorable, gradual cooling
aloft occurs, and the low-level shear increases substantially. The
fact that convergence will be subtle may be beneficial to the
supercell tornado threat, and deepening bands of convection may
eventually produce tornadoes from northern LA into central MS. Even
if storms in this area remain isolated, impressive hodographs with
0-1 SRH over 300 m2/s2 will favor supercells and tornadoes, perhaps
tracking for long distances given the lack of cold/stable air.
Therefore despite perhaps a weaker model signal over these southern
areas, the Moderate Risk has been maintained.

 

[cincywx]

latest disco notes the moderate risk may be adjusted northward across AR tmrw, and also hints at the conditional nature of the threat further to the south. pretty good disco.

 

[Timhsv]

Low -level moisture return vigorously underway from the GOM

 

[Taylor Campbell]

The 18z HRRR was monstrous.

 

[The Nino]

18z HRRR printing some nasty UH Streaks

 

[UncleJuJu98]

I'd be beating a dead horse... But that 18z run is very alarming. Jumping on with @The Nino and @Taylor Campbell

Id expect a high risk if trends continue.
As Casuarina calls them which I'm starting to like the term they're maybe multiple tornado families potentially a significant or two.

 

[ashtonlemleywx]

NAM 3k seems to hint at a preconfluence band forming well ahead of the rest of the convection. Don't be surprised to see a few discrete cells in Mississippi ahead of the main blob of convection a few hours before Sunset.

Those early preconfluence bands have snuck up on me so many times. It'll form before I plan to leave and I'll have to rush out to door as quick as I can once it pops up on radar. CAMs have struggled lately picking up on these early cells.

18z HRRR is picking up what I was referring to and what 12z NAM 3k was picking up. I think these prefrontal cells could start firing off as early as 3-4pm.

If it keeps this look we will see a high risk issued.

 

[ashtonlemleywx]

Holy excrement

 

[UncleJuJu98]

 

[ashtonlemleywx]

Almost every sounding I clicked on 18z HRRR had a PDS TOR. Absolute monster if it verifies.

 

[UncleJuJu98]

Almost every sounding I clicked on 18z HRRR had a PDS TOR. Absolute monster if it verifies.

Kinda curious to the fail modes, this event doesn't have the same fail modes it seems as the last two forecasted major events in the southeast.

 

[tornado examiner]

Kinda curious to the fail modes, this event doesn't have the same fail modes it seems as the last two forecasted major events in the southeast.

C a p…god that word is a curse…that doesn’t seem to be an issue for Friday at all though…

 

[tornado examiner]

For once the cap isn’t gonna lead to an event underperforming…

 

[UncleJuJu98]

C a p…god that word is a curse…that doesn’t seem to be an issue for Friday at all though…

Thinking a limiting factor maybe lack of actual initiation of storms in the warm sector although the HRRR under forecasted in the past two major forecasted events. And with this one it's already gungho. So id mark that one out...

Maybe mid level lapse rates being on the meager side or low level lapse rates? Doesn't need phenomenal low level lapse rates in the south though. And with the cold air advection in the mid levels I'd say mid level lapse rates should be fine.

Maybe a messy storm mode?

 

[tornado examiner]

Thinking a limiting factor maybe lack of actual initiation of storms in the warm sector although the HRRR under forecasted in the past two major forecasted events. And with this one it's already gungho. So id mark that one out...

Maybe mid level lapse rates being on the meager side or low level lapse rates? Doesn't need phenomenal low level lapse rates in the south though. And with the cold air advection in the mid levels I'd say mid level lapse rates should be fine.

Maybe a messy storm mode?

Yeah but even with the messy storm mode with how primed the environment should be for strong tornadoes we’ll still see those no matter what. So…imo…a high risk…is likely…but not guaranteed

 

[UncleJuJu98]

Yeah but even with the messy storm mode with how primed the environment should be for strong tornadoes we’ll still see those no matter what. So…imo…a high risk…is likely…but not guaranteed

I think a expansion of the moderate is definitely gunna happen. They'll wait to pull the high risk in the afternoon tommorow though before the event if they do.